1. Field
One or more embodiments of the present invention relate to a method, medium, and apparatus encoding an audio signal, and more particularly to, a method, medium, and apparatus encoding a scalable wideband audio signal.
2. Description of the Related Art
Various applications of an audio communication and enhancement of a network transmission speed have resulted in an increase in demand for a high quality audio communication. Transmission of a wideband audio signal having a bandwidth between 0.05 kHz˜7 kHz that has better performance in terms of naturalness and articulation than a conventional audio communication bandwidth between 0.3 kHz˜3.4 kHz is needed.
A packet switching network that transmits data in units of packets may cause channel congestion, resulting in a packet loss and sound degradation. To address these problems, technologies for concealing damaged packets have been used, but these do not contribute to a fundamental solution.
Therefore, research into a scalable wideband audio encoding technology capable of effectively compressing a wideband audio signal and overcoming channel congestion has been recently conducted.
FIG. 1 is a block diagram of a conventional scalable codec. Referring to FIG. 1, the conventional scalable codec comprises a core layer codec 100, a subtractor 110, and an error signal encoder 120.
The core layer codec 100 encodes an input signal IN and decodes an encoding result. The subtractor 110 subtracts the encoding result that is output by the core layer codec 100 from the input signal IN. The error signal encoder 120 encodes an error signal that is output by the subtractor 110. Therefore, it is possible to enhance a signal to noise ratio (SNR) of a signal in the same band.
FIG. 2 is a block diagram of another conventional scalable codec. Referring to FIG. 2, the conventional scalable codec comprises a down-sampling unit 200, a low frequency band codec 210, an up-sampling unit 220, a high frequency band restoring unit 230, an adder 240, a subtractor 250, and an error signal encoding unit 260.
The down-sampling unit 200 down-samples an input signal IN and outputs a signal in a slightly lower band than that of the input signal IN as a core layer signal. For example, the band of the input signal IN is 8 kHz, and the band of the down-sampled signal is 6.4 kHz. The low frequency band codec 210 encodes the down-sampled signal that is the core layer signal and decodes an encoding result. An example of the low frequency band codec 210 is an adaptive multi rate-wideband (AMR-WB) codec. The up-sampling unit 220 up-samples an output of the low frequency band codec 210. The high frequency band restoring unit 230 restores a signal in a band that is encoded in the low frequency band codec 210. The adder 240 adds an output of the up-sampling unit 220 to an output of the high frequency band restoring unit 230. The subtractor 250 subtracts an output of the adder 240 from the input signal IN that is an original signal. The error signal encoding unit 260 encodes an error signal that is an output of the subtractor 250. Therefore, it is possible to enhance an SNR of a signal as a whole.
FIG. 3 is a block diagram of another conventional scalable codec. Referring to FIG. 3, the conventional scalable codec comprises a band dividing unit 300, a low frequency band codec 310, a high frequency band codec 320, first and second subtractors 330 and 340, and an error signal encoding unit 350.
The band dividing unit 300 equally divides a frequency band of an input signal IN and outputs a low frequency band signal and a high frequency band signal. The low frequency band codec 310 encodes the low frequency band signal that is a core scalable signal and decodes an encoding result. The high frequency band codec 320 encodes the high frequency band signal and decodes an encoding result. The high frequency band signal is additionally encoded, thereby enhancing sound quality. The first subtractor 330 subtracts an output result of the low frequency band codec 310 from the low frequency band signal. The second subtractor 340 subtracts an output result of the high frequency band codec 320 from the high frequency band signal. The error signal encoding unit 350 encodes an error signal that is output by the first and second subtractors 330 and 340. Therefore, it is possible to enhance the SNR of a signal in a whole band.